1. Field of the Invention
The present invention relates to image forming apparatuses that form images with electrophotography, such as copying machines, printers, fax machines, and multifunction machines.
2. Description of the Related Art
Some image forming apparatuses employing electrophotography such as copying machines or printers include an intermediate transfer belt as a transfer belt. An image forming apparatus including an intermediate transfer belt forms full-color images by performing a first transfer process and a second transfer process.
In the first transfer process, a toner image formed on the surface of the electrophotographic photoconductor is first-transferred to the intermediate transfer belt. The first transfer process is repeatedly performed on toner images of different colors, whereby the toner images of multiple colors are formed on the surface of the intermediate transfer belt. In the second transfer process, the toner images of multiple colors are collectively transferred to the surface of a transfer medium such as a paper sheet. The toner images that have been transferred to the transfer medium are subsequently fixed by a fixing unit, whereby a full-color image is obtained.
Examples usable as a transfer device of an image forming apparatus include transfer devices having, for example, a roller shape, a blade shape, or a brush shape. These transfer devices are contact members that come into contact with the inner peripheral surface of the intermediate transfer belt at a position at which the members are located opposite the corresponding photoconductors. Among the above-described transfer devices, a brush-shaped transfer device includes multiple conductive fiber threads and the individual fibers are independently capable of touching the inner peripheral surface of the intermediate transfer belt. The use of the brush-shaped transfer device thus reduces unevenness in contact-related properties that would result from the use of a roller-shaped or blade-shaped transfer device. Thus, the transfer device can more evenly come into contact with the inner peripheral surface of the intermediate transfer belt. The brush-shaped transfer device thus facilitates reduction of image defects that can occur during the first transfer process such as unevenness in density.
Japanese Patent Laid-Open No. 2011-248385 discloses an image forming apparatus that includes a brush-shaped transfer device as a transfer device. In the brush-shaped transfer device disclosed in Japanese Patent Laid-Open No. 2011-248385, multiple conductive fiber threads constituting a brush are supported by a metal holder made of stainless steel (holding member) using a double-sided adhesive tape. The metal holder is fixed and the conductive fiber threads constituting the transfer device come into contact with the back surface of the intermediate transfer belt using their elasticity.
In the above-described image forming apparatus, however, some of conductive fiber threads of the brush-shaped transfer device may be disposed so as to protrude upstream from a contact area, over which the intermediate transfer belt and the photoconductor drum come into contact with each other, in the direction in which the intermediate transfer belt moves. Conductive fiber threads disposed so as to protrude upstream from the contact area cause an electric field in a gap between the photoconductor drum and the surface of the intermediate transfer belt and the electric field causes discharging (pre-discharging). This discharging may cause a streak-like image defect.
On the other hand, if a conductive fiber thread receives force acting in the direction in which the intermediate transfer belt moves as a result of the conductive fiber rubbing against the intermediate transfer belt, the conductive fiber thread may come out of the holding member or may be displaced over the holding member.